Ophthalmic surgeons work within a very small operating field upon organs whose tissues are complex and delicate. Cuts made during surgery must be precise as to length, direction and depth, requiring surgical knives of unsurpassed sharpness and maneuverability.
During surgery, there are times when particular knives, set to particular cutting depths, must be used. Often, it is necessary to change the depth of cut during surgery. Depending upon the method originally used to set the original depth of cut, it may be necessary to interrupt the surgery to make the needed changes. Where the depth of cut is simply to be increased by a selected amount, it is necessary for the surgeon to then calculate the new depth setting by adding the additional depth to the original setting and then resetting the knife to the new setting.
Surgical knives with micrometer settings are well-known in the art. U.K. Patent 2 113 550 (Kemp) typifies a surgical knife having a cutting blade which is extendible from the body of the knife by rotating the knife handle with respect to the knife body. U.S. Pat. No. 4,898,170 (Hofmann, et al.) teaches and describes a knife which incorporates a micrometer mechanism coupled to an offset head which holds a surgical cutting blade. U.S. Pat. No. 4,516,575 (Gerhard, et al.) teaches and describes a surgical knife with a micrometer mechanism used to measure the advance of the cutting blade, with provision to recalibrate the micrometer to accommodate variations in blade or blade holder configuration. U.S. Pat. No. 4,499,898 (Knepshield, et al.) teaches and describes a surgical blade holder having a micrometer-like mechanism to advance a cutting blade and a measuring scale usable to determine the depth of cut as the blade is advanced.
The Kemp (U.K.), Hofmann, et al., Gerhard, et al. and Knepshield, et al. references all show surgical knives which may be set to cut to a predetermined depth by advancing the cutting blade beyond a "foot" formed or positioned at one end of the knife. Once the cutting depth is set, however, the blade must be left exposed, as the only provision for moving the blade into the handle is to retract the blade past the foot.
Gerhard, et al. teach and describe a method for zeroing the micrometer scale when the leading edge of the cutting blade is aligned with the foot.
The distance the cutting blade extends from the knife holder is often set prior to surgery, and while the knife is not being used, it is desirable to protect the cutting blade from accidental contact with the hands or clothing of operating room personnel, and from damage that may occur from being dropped or contacted by other instruments. Loss of such a knife due to accident often means that the surgical procedure must be halted until another knife can be obtained and set for the same cutting depth as the original knife.
In U.S. Pat. No. 3,176,395, there is described a photoengraver's knife having a blade which can be fully withdrawn into the hollow handle of the knife, to protect both the blade and users of the knife between cutting operations.
The need then exists for an ophthalmic surgical knife which allows the depth of cut to be preset and thereafter to be changed during surgery without requiring an interruption to the surgical procedures.
The need also exists for a system of resetting the depth of cut which allows the surgeon conveniently to increase the depth of the cut by a chosen dimension without calculating and setting a new cutting depth.
The need also exists for a surgical knife with the capability of allowing the depth of cut to be set and, thereafter, allowing the blade to be covered or protected in a manner which does not affect the depth setting.